DESCRIPTION: These investigators have recently identified two closely related gammaherpesviruses present in retroperitoneal fibrosis lesions of immunosuppressed macaques. Preliminary data indicate that these newly discovered viruses (termed RFHV) are the simian counterparts of human herpesvirus 8, which is associated with Kaposi s sarcoma. In this application, the investigators propose to investigate the overall genomic structure of RFHV, to identify and characterize the RFHV homologs of cellular cytokine-like genes found in the HHV-8 genome, and to determine the prevalence of RFHV in retroperitoneal fibrosis lesions.